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A B S T R A C TThis paper considers the use of an ensemble Kalman filter to correct satellite radiance observations for state dependent biases. Our approach is to use state-space augmentation to estimate satellite biases as part of the ensemble data assimilation procedure. We illustrate our approach by applying it to a particular ensemble scheme-the local ensemble transform Kalman filter (LETKF)-to assimilate simulated biased atmospheric infrared sounder brightness temperature observations from 15 channels on the simplified parameterizations, primitive-equation dynamics (SPEEDY) model. The scheme we present successfully reduces both the observation bias and analysis error in perfect-model simulations.

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This paper evaluates a strategy for the assimilation of satellite radiance observations with the local ensemble transform Kalman filter (LETKF) data assimilation scheme. The assimilation strategy includes a mechanism to select the radiance observations that are assimilated at a given grid point and an ensemblebased observation bias-correction technique. Numerical experiments are carried out with a reduced (T62L28) resolution version of the model component of the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS). The observations used for the evaluation of the assimilation strategy are AMSU-A level 1B brightness temperature data from the Earth Observing System (EOS) Aqua spacecraft. The assimilation of these observations, in addition to all operationally assimilated nonradiance observations, leads to a statistically significant improvement of both the temperature and wind analysis in the Southern Hemisphere. This result suggests that the LETKF, combined with the proposed data assimilation strategy for the assimilation of satellite radiance observations, can efficiently extract information from radiance observations.

The definition and derivation of a 5-yr, 0.1258, 3-hourly atmospheric forcing dataset that is appropriate for use in a Land Data Assimilation System operating across South America is described. Because surface observations are limited in this region, many of the variables were taken from the South American Regional Reanalysis; however, remotely sensed data were merged with surface observations to calculate the precipitation and downward shortwave radiation fields. The quality of this dataset was evaluated against the surface observations available. There are regional differences in the biases for all variables in the dataset, with volumetric biases in precipitation of the order 0-1 mm day 21 and RMSE of 5-15 mm day 21 , biases in surface solar radiation of the order 10 W m 22 and RMSE of 20 W m 22 , positive biases in temperature typically between 0 and 4 K depending on the region, and positive biases in specific humidity around 2-3 g kg 21 in tropical regions and negative biases around 1-2 g kg 21 farther south.

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ResumoO objetivo desta pesquisa é estudar os ciclones e os padrões de circulação atmosférica a eles associados no Oceano Atlântico Sul, próxima à costa das Regiões Sul e Sudeste do Brasil, usando dados da Reanálise ERA-Interim nos meses de outubro a abril dos anos de 2003 a 2013. Foi desenvolvido um método objetivo para obter as datas, a localização e a intensidade dos ciclones, o que permitiu gerar compostos de algumas variáveis meteorológicas. Os resultados mostraram que em média ocorreram 17 casos de ciclones entre os meses de outubro a abril e que o período de vida dentro da região de estudo chegou até a 8 dias em alguns casos. O período de out/08 a abr/09 chama atenção por ter apresentado 27 casos. Os compostos para o período mostraram que a combinação de difluência no escoamento em altos níveis, associada a um cavado em médios níveis e a presença de anomalias positivas do vento zonal são favoráveis à formação de ciclones no Atlântico Sul, próximo à costa das Regiões Sul e Sudeste do país. A convergência do escoamento em baixos níveis é decisiva para estimular a ciclogênese na região. O estudo de caso mostrou uma aplicação da ferramenta desenvolvida que pode ter utilidade no aperfeiçoamento dos modelos numéricos de previsão desse tipo de sistema meteorológico.Palavras-chave: ciclones, ciclogêneses no Oceano Atlântico Sul, reanálise ERA-Interim. Cyclones and Atmosferic Circulation Patterns Study in the South Atlantic Ocean Near the Coast of South and a Southest of Brazil Using Reanalysis Era-Interim Data AbstractThe main objective of this research is to study the cyclones, and the atmospheric circulation pattern associated with them, occurring in South Atlantic Ocean, using data from ERA-Interim Reanalysis from October to April in the [2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013] period. An objective method was developed and applied to identify the dates, location and intensity of cyclones, which allowed to generate composites of some meteorological variables. The results showed that, on average, 17 cases of cyclones occurred in the months from October to April and the life within the studied area reaches up to 8 days.The period of October/2008 to April /2009 calls attention for recording 27 cases. Composites for the entire period showed a combination of the difluence in the flow at upper levels, associated with an mid-tropospheric trough and the presence of positive zonal-wind anomalies are favorable to formation of cyclone in the Atlantic Ocean near South and Southeastern Brazil. Convergence of low-level flow were decisive to stimulate cyclogenesis in the region. The case studied showed an application of the developed tool that can be useful in improving the numerical prediction models of this type of weather system.